The G chord (major): notes G B D, degrees 1 – 3 – 5. Guitar shapes: 320003, 355433, xx5787, x-10-9-7-8-7.
A chord is the root plus degrees above it, most often stacked in thirds. Major and minor differ only in the lower third: a major third (M3) sounds bright, a minor third (m3) sounds sad. Pick a chord and a root to see its degrees and intervals, and its shapes.
m — minor, M — major, P — perfect, A — augmented interval; the number is the degree count. m3 is 3 semitones, M3 is 4, P5 is 7
G Gm G5 G7 Gm7 Gmaj7 Gsus2 Gsus4 Gadd9 G6 Gm6 G9 Gdim Gdim7 Gm7♭5 Gaug